AD 90-23-12
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | The Boeing Company | 737-300 Series | Airworthiness Directives; BOEING Model 737-300 and 737-400 Series Airplanes |
| aircraft | The Boeing Company | 737-400 Series | Airworthiness Directives; BOEING Model 737-300 and 737-400 Series Airplanes |
Unsafe Condition
Auxiliary power unit (APU) rotor failure resulting from an undetected EGT overtemperature condition.
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Required Actions
Modify the APU instrumentation wiring to ensure continuous flight-compartment APU exhaust gas temperature (EGT) indication following a shutdown, in accordance with Boeing Service Bulletin 737-49-1071 or an approved method. An alternate means of compliance or adjustment may be used if approved by the FAA.
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Compliance Time
Within 1,000 hours time-in-service after May 29, 1990 for Model 737-400 series; within 1,000 hours time-in-service after December 11, 1990 for Model 737-300 series.
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Affected Aircraft
Boeing Model 737-300 and 737-400 series airplanes listed in Boeing Service Bulletin 737-49-1071 dated May 10, 1990.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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